High-throughput drug screening identifies the ATR-CHK1 pathway as a therapeutic vulnerability of CALR mutated hematopoietic cells.

Mutations of calreticulin (CALR) are the second most prevalent driver mutations in essential thrombocythemia and primary myelofibrosis. To identify potential targeted therapies for CALR mutated myeloproliferative neoplasms, we searched for small molecules that selectively inhibit the growth of CALR mutated cells using high-throughput drug screening. We investigated 89 172 compounds using isogenic cell lines carrying CALR mutations and identified synthetic lethality with compounds targeting the ATR-CHK1 pathway. The selective inhibitory effect of these compounds was validated in a co-culture assay of CALR mutated and wild-type cells. Of the tested compounds, CHK1 inhibitors potently depleted CALR mutated cells, allowing wild-type cell dominance in the co-culture over time. Neither CALR deficient cells nor JAK2V617F mutated cells showed hypersensitivity to ATR-CHK1 inhibition, thus suggesting specificity for the oncogenic activation by the mutant CALR. CHK1 inhibitors induced replication stress in CALR mutated cells revealed by elevated pan-nuclear staining for γH2AX and hyperphosphorylation of RPA2. This was accompanied by S-phase cell cycle arrest due to incomplete DNA replication. Transcriptomic and phosphoproteomic analyses revealed a replication stress signature caused by oncogenic CALR, suggesting an intrinsic vulnerability to CHK1 perturbation. This study reveals the ATR-CHK1 pathway as a potential therapeutic target in CALR mutated hematopoietic cells.

A phase III randomized, multicentre, double blind, active controlled trial to compare the efficacy and safety of two different anagrelide formulations in patients with essential thrombocythaemia - the TEAM-ET 2·0 trial.

Anagrelide is an established treatment option for essential thrombocythaemia (ET). A prolonged release formulation was developed with the aim of reducing dosing frequency and improving tolerability, without diminishing efficacy. This multicentre, randomized, double blind, active-controlled, non-inferiority trial investigated the efficacy, safety and tolerability of anagrelide prolonged release (A-PR) over a reference product in high-risk ET patients, either anagrelide-naïve or -experienced. In a 6 to 12-week titration period the individual dose for the consecutive 4-week maintenance period was identified. The primary endpoint was the mean platelet count during the maintenance period (3 consecutive measurements, day 0, 14, 28). Of 112 included patients 106 were randomized. The mean screening platelet counts were 822 × 109 /l (95% confidence interval (CI) 707-936 × 109 /l) and 797 × 109 /l (95% CI 708-883 × 109 /l) for A-PR and the reference product, respectively. Both treatments effectively reduced platelet counts, to mean 281 × 109 /l for A-PR (95% CI 254-311) and 305 × 109 /l (95% CI 276-337) for the reference product (P < 0·0001, for non-inferiority). Safety and tolerability were comparable between both drugs. The novel prolonged-release formulation was equally effective and well tolerated compared to the reference product. A-PR provides a more convenient dosing schedule and will offer an alternative to licensed immediate-release anagrelide formulations.

Inhibition of related JAK/STAT pathways with molecular targeted drugs shows strong synergy with ruxolitinib in chronic myeloproliferative neoplasm.

This study aimed to assess the antitumour effects, molecular mechanisms of action, and potential synergy of ruxolitinib with sorafenib, KNK437, dasatinib, and perifosine, in Philadelphia-negative chronic myeloproliferative neoplasms (MPN). Cytotoxic and cytostatic effects of the different compounds were determined in the JAK2 V617F-positive cell lines, HEL and Ba/F3 (JAK2V617F EPOR) , and in primary mononuclear and bone marrow CD34-positive cells from 19 MPN patients. Ruxolitinib [50% inhibitory concentration (IC50 )(PV)  = 15 nmol/l], as well as sorafenib (IC50 PV=8µmol/l), KNK437 (IC50 PV=100µmol/l ), and perifosine (IC50 PV=15µmol/l ), were able to inhibit proliferation in cell line models and in primary cells from MPN patients. Dasatinib, KNK437, and sorafenib showed a strong synergistic effect in combination with ruxolitinib [combination index (CI)(PV)  < 0·3]. Western blot confirmed that ruxolitinib blocked ERK, and consequently STAT5 activation, sorafenib inhibited ERK, P38 and STAT5, dasatinib blocked SRC and STAT5, and KNK437 decreased the stability of the JAK2 protein, reducing its expression. Inhibiting JAK2-related proliferative pathways has the potential to inhibit cell proliferation in MPNs. Furthermore, the combination of ruxolitinib with inhibitors that target these pathways has a strong synergistic effect, which may be due to decreased activation of the common effector, STAT5.

Cerebral infarct in a patient with a history of systemic arterial and venous thrombosis from essential thrombocythemia.

Although essential thrombocythemia (ET) may involve thrombotic complications, including arterial or venous thrombosis, there are no reports of major vascular complications, including both arterial and venous thrombosis, in a patient with ET. We report on a patient with a cerebral infarction affecting the right lateral thalamus and a stenotic lesion of the right posterior cerebral artery. This arterial thrombotic event may be related to ET, which was based on results of a bone marrow biopsy specimen. The patient had experienced previous events of thrombosis, splenic infarction with venous thrombosis, and myocardial infarction. The cause of recurrent ischemic events involving both arterial and venous systems may be sustained elevation of platelet counts. Previous thrombosis is an established risk factor for rethrombosis in patients with ET. Efficient cytoreductive therapy with an antiplatelet agent should be considered for the prevention of recurrent thrombosis.

[Clinical experience of urological surgery of the patients with hemostatic disorder or hemolytic disease].

This report deals with clinical experience of urologic surgery of patients with hemostatic disorder or hemolytic disease. In the past 5 years from May 1986, 14 operations were conducted in our clinic on 13 patients, consisting of 4 with von Willebrand disease (vWd), 1 with hemophilia B, 4 who had warfarin administration, 3 with essential thrombocythemia and 2 with spherocytosis. Almost all patients were treated hematologically before the urological operations. Except in 1 case, the post-operative course was favorable and under hematologic control. Massive bleeding in 1 case was obviously attributable to over-dosage of warfarin. It is difficult to determine the optimal dose of warfarin under an unstable hemostatic condition during the operation and recovery periods. However, it is possible to carry out urologic surgery for these patients under appropriate hematologic control, and ESWL was safely performed without medical treatment on 3 patients; 1 with vWd, 1 treated with warfarin and 1 with spherocytosis.